A couple of people have pointed out that the syntax you supplied is not quite correct.

With that said, once you correct the syntax, the command will find all files (-type f) and search each file for the string ACP11_CTRL, ignoring case and your output will only show you the name of the file that matched.

The short answer is, it will give you a list of files containing the string ACP11_CRTL.

This is how I'd write what you seem to be after. Also, this would run grep one time instead of once for every file:

grep -il ACP11_CTRL `find . -type f`

First, the stuff inside the backticks (find . -type f) is evaluated. That is, a list is created of all ordinary files ("-type f") in the current directory (".") or any subdirectory. (By default, "find" searches subdirectories). Actually, it'll be a list of the paths to the files.

The list of file paths is then appended to the grep command which will ignore case ("-i") and just spit out the file names ("-l") that contain the string "ACP11_CTRL".

The output will be the paths of the files that contain the string. For example, if there's a match in the current directory, the output would be:
./file_name
If there's a match three levels down, the output would be:
./first_directory/second_directory/third_directory/f ile_name

It will look in every file, in the current working directory, for the ACP11_CTRL string whether upper or lower case and print the file name if the match is found. The search is supposed to stop in each file after the first match.

hi
i think that you mean
find . -type f -exec grep -il ACP11_CTRL {} \;
means find any word (ACP11_CTRL) into any file not a directory and in other words........ use this name of file(from find command) as input {} for grep command to search about ACP11_CTRL (i- Ignores the case (uppercase or lowercase) of letters when making comparisons.
-l Lists (once) which contain matching lines)